This invention relates to a display device, and more particularly to an active matrix type liquid crystal display device with semiconductor elements, which includes destaticizing elements for protecting the semiconductor elements and insulating films from breakage through static electricity.
FIG. 10 is a schematic plan view, showing a circuit provided on an active element substrate incorporated in the conventional liquid crystal display device. A plurality of pixel electrodes (not shown) which constitute a display area, and thin film transistors (not shown) each connected to a corresponding one of the pixel electrodes are respectively arranged in a matrix on the active element substrate 1. On the active element substrate 1, there are also provided a plurality of scanning lines 4 each for supplying scanning signals to the corresponding thin film transistors, a plurality of data lines 5 each for supplying data signals to the corresponding thin film transistors, a plurality of auxiliary capacitance lines 6 extending parallel to the scanning lines 4 and forming auxiliary capacitance portions between themselves and the pixel electrodes, a plurality of input lines 7 arranged in a lower right portion (in FIG. 10) of the substrate, an annular short-circuiting line 8 located around the pixel electrodes which form the display area, and a plurality of destaticizing elements 9, each adjacent pair of which are arranged parallel to each other between the short-circuiting line 8 and a corresponding one of the data lines 5.
The right ends of the scanning lines 4 extend to a semiconductor chip mounting area 10 located at a right portion of the substrate 1 and indicated by the broken line. The lower ends of the data lines 5 extend to a semiconductor chip mounting area 11 located at a lower portion of the substrate 1 and indicated by the broken line. The upper ends of the data lines 5 extend to the upper end of the substrate 1. The left ends of the auxiliary capacitance lines 6 are connected to a common line 12. The extended ends of some input lines 7 extend to the semiconductor chip mounting area 10, while the extended ends of the other input lines 7 extend to the semiconductor chip mounting area 11. The upper and lower ends of the left side of the short-circuiting line 8 are connected to the common line 12.
Suppose, for example, that in the liquid crystal display device constructed as above, static electricity of high potential is applied from the outside to an upper end portion of the leftmost data line 5 located an upper end surface of the active element substrate 1. Then, the two destaticizing elements 9 connected to the leftmost data line 5 become conductive, whereby the short-circuiting line 8, the common line 12 and the auxiliary capacitance lines 6 come to have the same potential as the leftmost data line 5. At this time, the other destaticizing elements 9 connected to the other data lines 5 also become conductive and come to have the same potential as the short-circuiting line 8, the common line 12 and the auxiliary capacitance lines 6. Thus, the short-circuiting line 8, the common line 12, the auxiliary capacitance lines 6 and all data lines 5 come to have the same potential. This operation is performed when any one of the data lines 5 is charged with static electricity. Accordingly, the potential of the static electricity applied to the data line is lowered since it is guided to the short-circuiting line 8, the common line 12, the auxiliary capacitance lines 6 and the other data lines 5. Thus, the thin film transistor and the insulating film connected to the charged data lines 5 can be protected from breakage due to the static electricity.
The destaticizing element 9 is usually provided in the form of a diode which has an anode electrode connected to the short-circuiting line side, and a cathode electrode connected to the data line 5 side. This kind of destaticizing element 9, however, cannot work well in response to an electrostatic pulse which extremely and abruptly rises to a high potential. Therefore, when such a high-potential electrostatic pulse is applied, it flows through the data lines 5 only, thereby breaking the thin film transistors and/or or insulating films connected thereto. Thus, the destaticizing elements 9 cannot completely protect the transistors or insulating films.